1. Field of the Invention
This invention relates to an air intake of an aircraft nacelle that integrates optimized hot air injection means for frost treatment.
2. Description of the Related Art
In a known manner, as illustrated in FIG. 1, a propulsion system 10 of an aircraft 11, for example connected under the wing by means of a mast 12, comprises a nacelle 14 in which a power plant is arranged in an essentially concentric manner. The longitudinal axis of the nacelle is referenced 16.
The nacelle 14 comprises an inside wall that borders a pipe with an air intake 18 at the front that makes it possible to channel the air in the direction of the power plant.
This invention relates more particularly to a nacelle that integrates a frost treatment process that uses hot air in contact with the inside wall of the air intake 18, in particular hot air that is drawn off from the engine 19.
According to an embodiment that is known from the documents FR-2,813,581 and U.S. Pat. No. 6,443,395, illustrated in FIGS. 2 and 3A and 3B, a nacelle 14 comprises, on the inside, a partition that is called a front frame 20 that with the air intake 18 borders a pipe 22 that extends over the entire circumference of the nacelle and that has an essentially D-shaped cross-section in which the hot air circulates.
This pipe 22 is supplied with hot air by injection means 24.
The injected hot air makes a 360° passage around the pipe 22 before being discharged. In addition to a centrifugal action, the hot air circulates more on the outer side of the air intake referenced 28 in FIG. 2.
If the means 24 for injection of hot air are placed at the lowest point of the nacelle, the de-icing capacity is not homogeneous over the circumference. It quickly increases to reach a maximum value and then gradually decreases over the rest of the circumference, with an inconsistency of frost treatment at the lowest level.
Because of the centrifugal action and/or the non-homogeneous aspect of the temperature over the circumference, the temperature at the inner side 30 of the air intake cannot be adequate.
To remedy this possible inadequacy, it is possible to inject air that is hotter and/or with a higher flow rate.
However, this solution is not satisfactory because it is necessary to provide high-temperature-resistant materials for the front frame, the air intake and the optional acoustic treatment coverings. This aspect tends to reduce the selection of usable materials and generally imposes the use of heavy and relatively expensive materials.
As illustrated in FIGS. 3A and 3B, the injection means 24 can come in the form of a tube 32 that is perpendicular to the front frame that has one or more injection openings 34 that are oriented in the direction of circulation of the air that circulates in the pipe 22. In this case, the injection means generate, in the stream of less hot air that circulates in the pipe 22, a stream of just injected hot air whose boundary 36, indicated by dotted lines in FIGS. 3A and 3B, constitutes the exchange surface between these two air streams.
To improve the exchanges, a solution can consist in increasing the exchange surface by increasing the number of injection openings 34. However, in this case, the injection means are relatively bulky and produce significant pressure drops. In addition, increasing the number of injection openings while preserving an adequate injection rate in the pipe calls for increasing the necessary flow of hot air, which leads to increasing the necessary energy for its production and therefore the consumption of the aircraft.
According to another aspect, the greater the difference in temperatures between the injected hot air and the less hot air that circulates in the pipe, the less these two air streams are mixed although the stream of just injected hot air tends to impact the wall of the pipe with a very high temperature. Thus, two streams are obtained, one with a temperature that is significantly higher than the temperature that is necessary for frost treatment, and a second stream whose temperature is inadequate for said treatment.
To limit the impact temperature of the stream of just injected hot air, the documents FR-2,813,581 and U.S. Pat. No. 6,443,395 propose placing—behind the injection means 24—a mixer that comprises a nozzle-type tube that mixes the injected hot air with the less hot air that is already present and that circulates in the pipe 22. This solution has the advantage of reducing the maximum value of the temperature experienced by the wall of the pipe 22 and because of the mixing makes it possible to obtain a stream of hot air with an adequate temperature for frost treatment, having a flow rate that is significantly higher than that of the stream of just injected very hot air of the prior art without a mixer.
However, this mixer is not entirely satisfactory because it constitutes a supplementary part in addition to the injection means that induces a supplementary on-board weight and specific maintenance. However, if the injection means are accessible because of an access flap in the bottom part of the nacelle, the mixer is offset relative to said flap, although it is not easy to inspect it and it is often necessary to remove the air intake in case of malfunction, which calls for a substantial immobilization of the aircraft.